Field of the Invention
The present invention relates to a mixing system, and in particular to a magnetic mixing system and method.
Description of the Related Art
In the preparation of liquid components for biotech and pharmaceutical processing, it is important to perform mixing within a closed environment. The process of manufacturing a biological is very delicate and can fail due to a breach within a closed system because of bacterial or viral ingress. In many instances, certain chemicals must be blended into liquid to form a component of the process or must be continuously stirred in order to inhibit separation during the process. The process is controlled at every step to assure a constant temperature, balanced PH, and foreign substances stay out of the process. For example, it would be undesirable to have heat from a motor disrupting the process. It would also be undesirable to have a large opening in the system, and it would certainly be undesirable to stick one's hand, fingers or other foreign objects into or proximate the process or system. Further, undue shear or vibration will adversely affect the integrity of the system.
Some applications of a magnetic stirrer may be in a perfusion vessel or an aseptic separator device. Other uses may exist.
Long ago, i.e., at least as early as 1917, a magnetic stirrer was proposed by Stringham in U.S. Pat. No. 1,242,493, and later in 1942 improved by Rosinger in U.S. Pat. No. 2,350,534. The stifling element consisted of a rod shaped magnet inside and a neutral shell or covering around it. The magnet that caused the stirring element to rotate was U-shaped and had the poles pointing upward, and was rotatably mounted around a vertical axis, coinciding with a central point on the stirrer. The stirrer rod was simply dropped in the container, and allowed to sit on the bottom of the container.
However, it is much better to suspend the stirrer so that it does not touch the walls or bottom of the container. Touching the bottom or walls can subject the process to a grinding action, which is undesirable and can also serve to produce particulates. Similarly, creation of shear can be problematic for the cells within the process as well. Suspension also eliminates the need for lubrication, which can contaminate the culture. Accordingly, in U.S. Pat. No. 3,572,651 to Harker, the stir bar is suspended.
The controls for the stirrer and the driving force (a magnetic field) may be outside the container in which the cell culture or process is located. Since the stifling force is magnetic, no physical connection of the stir bar and the power source are required. Therefore, the container may be properly sealed and free from contaminants to maintain an aseptic environment.
In some conventional systems, a rod shaped internal magnet is placed within a container holding a fluid to be mixed. The rod shaped magnet may be free to roam across the bottom of the container, and may be coated with PTFE. The rod shaped internal magnet may be engaged by an external magnet located below the container and driven to rotate around an axis perpendicular to a longitudinal axis.
The conventional system may allow friction to occur between the internal magnet and an interior surface of the container when the internal magnet rests on an interior surface of the container and is driven to rotate by the external magnet. As a result, debris from the internal magnet may be released such as during irradiation of the mixer for decontamination. For example, the PTFE may begin to break down during irradiation, allowing the coating to crack and shed particles. In addition, the breakdown of the PTFE coating may allow the internal magnet to rust, which may result in additional particle shedding from both the rusting magnet.
In addition, getting the stirring device into the container without damaging the device or container and without contaminating the system can be a challenge. Because the stir bar extends horizontally (normal to the rod holding it), it can be difficult to get a large enough bar to effectively cause mixing inside the container.
The present mixing system may be useful in many ways, such as in aseptic mixing applications for cell culturing or other applications,
The conventional system may have other drawbacks as well.